Surface temperature sensors are known in the art; contact-type surface temperature sensors are designed to make contact with a surface in order to measure the temperature of the surface. For example, U.S. Pat. No. 4,859,081 describes one type of surface temperature sensor which includes a thin plate spring with a thermocouple junction on a central portion thereof. The plate spring is fixed at both of its ends to a support member so that the plate spring projects semicircularly in side elevation to form a temperature sensing portion. The plate spring and the thermocouple junction are brought into contact with the surface to be measured and are pressed against the surface to flatten slightly the semicircular portion of the plate spring. As a result, part of the plate spring and the thermocouple junction are engaged closely in press contact with the surface to be measured.
GB Application No. 932,260 (Pearce) relates to another type of surface temperature sensor having a thermocouple ring supported by an insulated disk which in turn is supported by a coil consisting of one of the two thermocouple materials. The sensor is pressed against a surface to be measured, whereby the thermocouple ring makes direct contact to the surface. The thermocouple ring and the insulated disk arrangement is capable of travel in a direction perpendicular to the surface due to the coil. The amount of travel is limited by an outer casing which surrounds the thermocouple ring.
Another type of surface temperature sensor is disclosed in U.S. Pat. No. 4,454,370 (Voznick) which shows a pair of side-by-side elongated coils that come into contact with one another at their ends to form a thermocouple junction. The surface temperature sensor further includes a protective sleeve supported by a coil which engages the surface to be measured prior to the thermocouple junction in order to ensure a safe rate of contact and thereby protect the thermocouple from damage. Once in contact with the surface, the thermocouple junction is further operable to move in a direction perpendicular to the surface via its secondary coils to make a direct press contact with the surface.
There are several drawbacks associated with the conventional contact-type surface temperature sensors enumerated above. In each of the above sensors, the thermocouple junction makes contact directly with the surface to be measured. When using conventional lap joints for thermocouples, wherein one of the thermocouple materials overlap the other to form the thermocouple junction, the lap joint prevents the junction from uniformly contacting the surface to be measured, thereby introducing a measurement error. Alternatively, when using a conventional butt joint to form the thermocouple junction, sputtering, flash, etc. can produce a buildup at the joint or a nonuniformity, such as a burr, may form on the surface and prevent the thermocouple junction from uniformly engaging the surface to be measured. Such direct contact of the thermocouple junction to the surface to be measured results in substantial thermal contact resistance. Any such contact resistance is in series with other thermal resistance and undesirably reduces the heat transfer between the surface to be measured and the sensor.
Another drawback associated with conventional surface temperature sensors is the use of an electrical insulating layer between the thermocouple junction and the junction holding apparatus. The insulating layer, although electrically insulating, contains a substantial thermal mass and thereby provides a thermal loading effect on the thermocouple junction, thereby resulting in thermal measurement error and a slow response time which thus requires contact with the surface to be measured to be maintained for an undesirably long period of time to ensure an accurate thermal measurement.
Yet another disadvantage associated with the conventional contact-type surface temperature sensors is the excessive thermal loading due to the travel stop. Such prior art protection includes semicircular housing walls which substantially encircle the thermocouple junction. The housing walls limit the distance the resilient thermocouple junction can be deflected when pressed against a large surface. The housing walls come in contact with the surface to be measured and, due to the substantial thermal mass of the housing walls, may modify the surface temperature. Therefore such prior art designs are undesirable because the housing walls may cause measurement error.
In view of the above shortcomings associated with convention contact-type surface temperature sensors, there is a need in the art for a rugged surface temperature sensor which reduces heat transfer errors and provides for miniaturization.